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Mineralma@er Derivedfromweatheredrock Parentmaterial(mineralma@eruponwhich soilforms) Organicma@er Air and water Humus: complex materials that have resisted decomposition and accumulate in soil 2.SoilParJcleSize,Texture,Structure Particle size Texture Influencehowsoilholdswaterand mechanicalproperJes Geography211(Fall2009) 10/27/09 1 Atom: nucleus contains positively charged protons and electrically neutral neutrons electron cloud of negatively charged electrons surrounding dense nucleus when the number of protons in nucleus equals number of electrons, atom is electrically neutral otherwise it is an ion and has a net positive or negative charge Ion: lost or gained one or more electrons, giving it positive or negative electrical charge Anion: negatively charged ion, which has more electrons than protons Cation: positively-charged ion, which has fewer electrons than protons SoilColloids <1/100,000mm colloidsnegaJvelycharged a@ractsoilnutrients(ionsinsoilwatermostlycaJonsposiJvelychargedions) ionsheldandgivenuptoplantsfornutriJonifinclosecontact SoilStructure
Granular: < 0.5 cm in diameter surface horizons where roots break apart through wetting/ drying and freeze/thaw Blocky: irregular blocks usually 1.5-5.0 cm diameter wetting/drying and freeze/thaw Geography211(Fall2009) 10/27/09 2 Prismatic: vertical columns up to cm long vertical cracking in soil Platy: thin, flat, horizontal plates compacted soils horizons where water moves laterally Massive: no visible structure hard to break apart Single Grained: individual particles that do not stick together sandy soils often in relatively unweathered layers 3.MechanicalProperJes
Rheology: Study of behaviour of material under stress Strain: Response to stress Viscous low internal friction/cohesion no threshold (moves as long as stress > 0) Fracture brittle behaviour Elastic body returns to original size/shape after stress strain recoverable rubber ball deforms as hits floor then recovers shape) Plastic strain begins after stress exceeds threshold strain not recoverable ball of clay falls to floor and sticks as deformed blob Soil behaves as either brittle solid/plastic/viscous depending on water content... Geography211(Fall2009) 10/27/09 3 Atterberg Limits
Liquid Limit: change from plastic to viscous fluid Plastic Limit: stops being plastic and becomes brittle solid Plasticity Index (PI): PI = LL PL quantifies range of moisture content within which soil has plastic properties continuously deformed when force applied, but retains new shape when force removed further reduction of moisture content causes soil to crumble under load and not deform plastically High PI: predominantly clay Lower PI: predominantly silt PI of 0: tend to have little or no silt/clay Highly plastic soils: ability to swell if given access to water cyclic shrink/swell behavior in upper portion of soil column, and cracks can extend to great depths damage foundations by pressure as swell with moisture increases or if cracking/ fracturing when drying 4.SoilDevelopment
Primary minerals: present in unaltered rock Secondary minerals: primary minerals altered by exposure to air and water Parent Material composition/structure of parent material Topography determines runoff/erosion Climate weathering climate determines vegetation (influences soil development) precipitation affects horizon development (translocation) Organisms organic matter decomposition/weathering/nutrient cycling Time Over time horizon development differentiates layers more mature soils have well-developed horizons Geography211(Fall2009) 10/27/09 4 O Horizon: top, organic layer leaf litter and humus (decomposed organic matter) A Horizon: seeds germinate and plant roots grow humus and mineral particles (dark colour) E Horizon: eluviation (leaching) layer light in color mostly sand/silt - lost clays and elements during eluviation B Horizon: illuviation layer clay and mineral deposits (iron, aluminum oxides, calcium carbonate etc.) received from above as water moves into soil C Horizon: slightly broken-up bedrock plant roots do not penetrate this layer; low organic matter R Horizon: unweathered rock SoilFormingFactors ParentMaterial Time Biological Climate Topography Humaninfluence (PhysicalWeathering) Rockstructure Joints Faults Folds ParentMaterial Rocktype Igneousandmetamorphic Sedimentary Temperature Freezethawcycles Fires OrganismsandvegetaJon Geography211(Fall2009) 10/27/09 5 (ChemicalWeathering) Mineralstabilitydependsoncrystalstructureand chemicalcomposiJon PrimaryProcesses Hydrolysiswaterreactswithmineralstomakeclay minerals(acidspresent) ChelaJonjoiningmetalionswithorganicsubstances OxidaJonelementlossesanelectron IonexchangeexchangeofionsbetweensoluJon andclays SoluJondissolvingminerals(carbonatesprimarily) ParentMaterial Time Ratesofrockandmineralweathering difficulttodetermine Developmentofsoilhorizons Ahorizonsdevelopquickly Bhorizonsdevelopslowly BiologicalFactors(plants) VegetaJonaffectssoilsintwoways: Soilstructure Soilchemistry ForestvsGrassland Foresthasgreaterleaching ForesthaslowerpH(acidic) ForesthasgreaterclaytranslocaJon Grasslandhashigherorganicma@eratdepth Geography211(Fall2009) 10/27/09 6 VegetaJonandSoilDistribuJon BiologicalFactors(animals) AboutofallmetabolicacJvityinsoilcomes frommicroorganisms(bacteria) Surfaceorganisms Compactsoil Addnutrientsviadroppings Smalleranimals Burrowingaeratesthesoilandincreaseswater infiltraJon Climate Themostimportantfactordeterminingthesoil properJes TemperatureandprecipitaJonmostimportant Waterdeliveredtosoilinfluencesweatheringand leaching TemperatureinfluencesratesofchemicalreacJons Forevery10Cincrease,reacJonratesincreaseby23 Jmes ManysoilproperJesshowtrendswithregional climate Organiccontent Claycontent Geography211(Fall2009) 10/27/09 7 ClimateandSoilDistribuJon SoilFormaJonandClimate (SlopeMagnitude) Slopeanddrainagemostimportant VerJcalextentofsoilchangeswithJme Topandbo@omofsoilcolumnarelowered Topbyerosion Bo@ombyweatheringandrootpenetraJon Topography Soildepthvarieswithslopeofland Steepslopehigherosion,li@lesoil Gentleslopeli@leerosion,moresoil Geography211(Fall2009) 10/27/09 8 (SlopeOrientaJonaspect) Aspectchangesmicroclimate Temperature EvaporaJon Topography Theamountoforganicma@eristhemost visiblechange EffectofAspect (posiJononslope) Topography Affectsdrainage Controlsweathering Topofslopesdrier,bo@omwe@er AffectsvegetaJonpresent ControlsaccumulaJonoforganicma@er Geography211(Fall2009) 10/27/09 9 HumanImpact NegaJve Erosion ReducJoninferJlity PolluJon PosiJve IncreaseinferJlity Improvedstructure Improveddrainage Contouredlandtominimizeerosion 5.SoilClassificaJon SoilClassificaJon Soiltaxonomy BasedonsoilproperJesandmorphology ManyclassificaJonsused DuetoregionalperspecJves Hierarchicalsystems Eachlevelbasedondifferentcriteria Geography211(Fall2009) 10/27/09 10 U.S.SoilTaxonomy Orders11 Suborders47 Greatgroups230 Subgroups1,200 Families6,000 Series15,000 12SoilOrdersU.S.ClassificaJon OxisolslaterizaJon AridisolssalinizaJon MollisolscalcificaJon Alfisols UlJsols SpodosolspodzolizaJon EnJsols IncepJsols VerJsols Histosols Andisols Gelisols Oxisols Geography211(Fall2009) 10/27/09 11 CalcificaJon PrecipitaJonandCalcificaJon SpodosolsandPodzolizaJon Geography211(Fall2009) 10/27/09 12 Classification schemes arrange objects in orderly fashion by placing into groups or "classes" according to similarity to each other. Order (10 Soil Orders) Shows which soil forming factors had most influence on soil formation Describes soil horizons Great Groups Delineated on basis of profile characteristics resulting from soil formation e.g. Great Groups within Chernozemic Order are Brown, Dark Brown, Black and Dark Gray (reflection of climate and vegetation) Subgroups Based on how strongly soil profile is developed as result of slope position and moisture Soil Series: Usually have same arrangement of horizons with similar minerals and organic mater (colour, texture, horizon thickness, and pH all similar) SoilClassificaJon(Canada) Canadian SoilOrders (1) Brunisol: immature soil commonly found under forested ecosystems presence of a B horizon that is brownish in color soils under dry pine forests of south-central B.C. are typically brunisols Geography211(Fall2009) 10/27/09 13 (2) Chernozem grassland ecosystems e.g., Canadian prairies dark in color (brown to black) and has an A horizon that is rich in organic matter (3) Cryosol high latitude soil common in tundra layer of permafrost within one meter of soil surface often cracks (4) Gleysol found in ecosystem that is frequently flooded or permanently waterlogged soil horizons show chemical signs of reduction Geography211(Fall2009) 10/27/09 14 (5) Luvisol another soil that develops under forests has calcareous parent material which results in high pH strong eluviation of clay from A horizon (6) Organic mainly composed of organic matter in various stages of decomposition common in bogs profiles of these soils have an obvious absence of mineral soil particles (7) Podzol coniferous forests poorly decomposed organic layer, an eluviated A horizon, and a B horizon with illuviated organic matter, clay, aluminum, and iron forested regions of southern Ontario and temperate rainforests of B.C. normally have podzolic soils Geography211(Fall2009) 10/27/09 15 (8) Regosol any young underdeveloped soil immature soils are common in geomorphically dynamic environments e.g., many mountain river valleys in British Columbia have floodplains with surface deposits that < 3000 years old - soils in these environments tend to be regosols (9) Solonetzic grassland soil where high levels of evapotranspiration cause deposition of salts at or near soil surface common in dry regions of prairies where evapotranspiration greatly exceeds precipitation movement of water to earth's surface causes deposition of salts when water evaporates (10) Vertisolic very clayey soils with lots of swelling clay minerals swelling clays because they increase in volume as gain moisture, and shrink as dry pronounced cracking as soils dry combined with surface soil falling into cracks obliterates well-defined horizons, mixing the soil to about 1m depth Geography211(Fall2009) 10/27/09 16 Canadian SoilOrders Geography211(Fall2009) 10/27/09 17 ...
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